raghav-reglobe commented on PR #69222:
URL: https://github.com/apache/doris/pull/69222#issuecomment-6657040441
@eldenmoon — this PR touches the Variant core, so two design choices are
worth your eyes before the auto-requested FE reviewers get to the Nereids half:
1. **Which call gets typed.** The template is attached by a sink-scoped
rewrite (`TypeVariantTemplateParse`): from the OLAP sink down to the
`parse_to_variant` / `try_parse_to_variant` call that feeds a templated column,
through VALUES, SELECT, CTE, UNION and derived-table shapes. A SELECT outside a
sink keeps its cast and the untyped call, and `SimplifyCastRule` is untouched.
The earlier draft typed the call in `SimplifyCastRule`; that missed the shapes
where the cast and the call never become adjacent.
2. **What crosses the wire.** `TScalarType.variant_template_paths` carries
the whole Schema Template in declaration order as `TVariantTemplatePath
{pattern, is_glob, is_decimal}` (renamed from the draft's
`TVariantDecimalPath`; precision and scale dropped — the emitted decimal's
width follows the text's own digits, and the column's cast decides the rest).
The BE matches a path the way the shredder does: first field in declaration
order, `==` for a literal, `fnmatch(FNM_PATHNAME)` for a glob; an object or an
array nested inside an array keeps its subtree off every declared path. The
struct exists on no release branch, and a BE that receives no paths behaves as
before.
If you would rather see the template matched elsewhere (for instance the
shredder's own matcher exposed to the parser), say so and I will rework it —
the BE text reader and its tests stay the same either way.
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